Note: Descriptions are shown in the official language in which they were submitted.
CA 02237964 1998-OS-15
WO 98/12371 PCT/US97/16505
YARNS OF COVERED HIGH MODULUS MATERIAL AND
FABRICS FORMED THEREFROM
Field of the Invention
The present direction is directed to yarns of
high modulus materials, such as polymer materials,
covered within a second material. The yarns can be
used to construct fabrics used in clothings for paper
making machines and other industrial fabrics.
3ackaround of the Invention
Paper machine clothing is the term for industrial
fabrics used on paper machines in the forming,
L0 pressing and drying sections. They are generally
fabricated with either polyester or polyamide
multifilaments and/or monofilaments woven on
conventional, large textile looms. These fabrics have
generally been fabricated by conventional weaving
techniques.
The primary function of all paper machine clothing
(PMC) is removal of water from the paper sheet. As
both the manufacturer of paper malting machine and
papermaker work to increase the speed of the
papermaking process and improve paper quality, new
barriers have been identified for PMC fabrics that
demand innovation in materials and fabric design.
Furthermore, the PMC manufacturer is also looking for
more efficient, production of PMC fabrics and enhancing
key quality characteristics of the same.
Today, paper making machines are attaining such
rapid speeds that the thickness of the fabric
structure is beginning to limit the rate of water
removal, especially in the forming section.
Insufficient dewatering results in low sheet strength.
SUBSTITUTE SHEET (RULE 26)
CA 02237964 1998-OS-15
WO 98/12371 PCTII1S97/16505
Sheet strength is critical for transferring and
maintaining sheet properties through the next, more
x
aggressive stages of sheet dewatering. One possible
solution is to lengthen the forming section of the
machine, but this is rather expensive and therefore of
limited viability. The other approach is for the PMC
manufacturer to produce thinner fabrics, but in a
weaving process the smallest possible dimensions are
the combined diameters of the filaments used in the
warp and chute directions. Criteria such as
dimensional stability, fabric strength and fabric life
result in a practical limit to the fineness of the
filament diameter and thus the overall thickness of
the fabric. In many PMC positions, a tradeoff of
these properties is not feasible or practical, and in
fact higher machine speeds actually require further
enhancement of these properties.
There is a definite need for high strength, low
weight, relatively thinner clothings than those which
are presently available.
The surface topography of PMC fabrics contributes
to the quality of the paper product. Efforts have
been made to create a smoother contact surface with
the paper sheet. However, surface smoothness of PMC
woven fabrics is limited by the topography resulting
from the weave pattern and the filament physical
properties. In a woven fabric (or knitted fabric),
smoothness is inherently limited by the knuckles
formed at the cross-over points of intersecting yarns.
High modulus materials are potential materials
for use in applications requiring high mechanical
properties and light weight. On a property-weight
basis, high modulus polymers have a distinct advantage
over metals and ceramics.
High modulus polymers are highly anisotropic, and
2
CA 02237964 1998-OS-15
WO 98/12371 PCTIITS97/16505
high modules is achieved only in the direction of
molecular chain orientation. In fact, properties
normal to the molecular axis exhibit considerably
lower values than the properties exhibited in the
longitudinal direction. As a result,.low shear and
compressive properties are exhibited in the direction
normal to the molecular axis.
Composite design concepts are known in the art in
order to compensate for the discrepancy in properties.
Representative is U.S. Patent No. 4,927,698 which
discloses yarns of a core of fire-resistant filaments
such as Kevlar~ and Nomex° within a sheath of
shrinkable staple fibers such as yarns which appear to
be chemically bonded to the fire-resistant core
through the reactions between a first cross-linkable
resin, a second cross-linkable resin, the
Kevlar~/Nomex~ component, and the staple fiber
component.
Summary of the Invention
The present invention is directed towards yarns
of covered high modules filament materials and fabrics
which are formed therefrom. The present invention is
intended to provide a composite filamentary material
which exhibits the advantages of high modules
materials while providing a means for compensating the
diminished properties exhibited by such fibers in the
direction normal to molecular chain orientation.
The present invention is a composite filament
structure wherein a high modules filament material is
covered with bicomponent filaments. The composite
filament structure has a first interior layer of high
modules filament material and a second exterior layer
of bicomponent fibers, the second exterior layer of
bicomponent fibers being covered around the first
3
CA 02237964 1998-OS-15
WO 98/12371 PCT/US97/I6505
interior layer of high modulus material along its
entire length. The entire surface area of the high
modulus material should be covered.
The bicomponent fibers of the present invention
may be either a sheath-core arrangement or a side-by-
side arrangement, with sheath-core being preferred.
It is further preferred that the sheath component have
a melting point lower than the core component.
Suitable bicomponent fibers include sheath-core
combinations of co-polyester/poly (ethyl.ene
terephthalate), polyamide/poly (ethylene
terephthalate),polyamide/polyamide,polyethylene/poly
(ethylene terephthalate), polypropylene/poly (ethylene
terephthalate), polyethylene/polyamide,
polypropylene/polyamide, thermoplastic
polyurethane/polyamide and thermoplastic
polyurethane/poly (ethylene terephthalate.
"Modulus", as used herein, refers to the tensile
modulus as defined by the slope of the initial linear
portion of the load extension response (stress-strain
curve) of a specimen deformed at room temperature.
High modulus material, as used herein, includes
high modulus polymers that exhibit tensile modulus
greater than about 250 of theory. Alternatively, a
high modulus polymer is one possessing a tensile
modulus greater than about 25 GPA. Encvclopedia of
Polymer Science 2d ed. vol 7, pt~. 699-722. It should
be noted that highly oriented polymer structures are
anisotropic, and as modulus is increased by raising
the degree of molecular chain orientation, modulus
decreases commensurately in other directions.
Suitable high modulus polymers include, but are
not limited to aramids such as poly (p- '
phenyleneterephthalamide), available from Dupont under
the tradename Kevlar~, other aramids such as Kermel~
4
CA 02237964 1998-OS-15
WO 98/12371 PCT/US97/16505
(available from Rhone-Poulenc) Arenka~, available from
Akzo, Nomex (available from DuPont), polyethylene
naphthalate (PEN), polyp-phenylene benzobisthiazole),
polyesters, glass, aromatic polyamide resins Arenka~,
an aramid available from Akzo, thermotropic
copolyesters such as Vectra~ (Celanese) and Xydar~
(Dart), high modules polyethylene fibers such as
Spectra 900 (Allied).
The skilled artisan should appreciate that there
are several ways in which the high modules interior
could be covered, such as braiding and wrapping. A
braid of bicomponent fibers around the high modules
interior provides a structure with good stability.
Wrapping the high modules fibers with the bicomponent
fiber material is another suitable method. Fibers
could be covered with either a single covering machine
or a double covering machine. In either case, the
core fibers are spirally covered at a selected pitch.
In constructing fabrics of the present invention,
advantage is taken of the unique structure of
bicomponent filament. The melting point of the sheath
component is lower than the melting point of the core
component, and lower than the melting point of -the
high modules interior. Improved structural integrity
is imparted by heating the fabric, which has been
formed from the yarns, which intersect each other in
the fabric, to a temperature in excess of the melting
point of the sheath but lower than the melting point
of the core and high modules interior, followed by
subsequent cooling. This process, hereinafter
> referred to heat fusion, causes the sheath components
of the bicomponent fibers to enter a softened state,
and accordingly, the yarns fuse together at contact
points when cooled to temperatures below the melting
point of the sheath material.. For the most part, such
5
CA 02237964 1998-OS-15
WO 98/12371 PCTlUS97/16505
contact points are the points where the yarns
intersect each other.
s
Due to the improved stability of the fabrics of
the present invention, it is believed that a single
layer fabric constructed of the composite yarns of-the
present invention could successfully run on a paper
making machine. That is, the present invention
provides a means for producing single layered fabrics
able to withstand the demanding conditions which paper
machine clothings are subjected to. Generally,
fabrics must be constructed of at least two layers to
insure that the fabrics have the necessary dimensional
stability and strength in order to withstand the
demanding running conditions.
The present invention could also be used as the
top laminate structure of a multilayer structure, and
it is believed that its use as such a layer would
offer advantages over conventional materials due to
reduced knuckle size on the surface of the fabric and
reduced caliper of the fabric. Reduced knuckle size
would create a smoother fabric surface, a feature
desired by paper makers. It is also possible that a
thinner fabric can be made using the high modulus
composite yarns of the present invention since the
excellent tensile properties possessed by high modulus
materials means that less material could be used to
attain the degree of strength possessed by
conventional fabrics. The present invention may also
be used as the base layer of a multilayer structure.
The improved dimensional stability of this layer makes
it well suited for this usage. Using a fabric
according to the invention as a base layer would
impart certain advantages to the overall fabric
construction. Because the composite yarns of the
present invention exhibit a relatively high degree of
6
CA 02237964 1998-05-15
WO 98/12371 PCT/US97/16505
strength along the axis of the yarn, the use of this
fabric layer as the base layer would provide the
stability and strength required of the overall fabric
structure. Therefore, less rigid materials could be
s
used in other fabric layers, enabling the paper maker
to, for example, select fibers of fine denier to
construct other layers. Accordingly, fabrics could
be
made thinner in this way as well. A thinner fabric
is
desirable since drainage properties would be improved.
In a preferred embodiment of the invention, the
yarns of the present invention are the sole
constituents of at least one layer of a clothing. In
the case of multiple layer clothing, at least one
layer is constructed of the yarns of the present
invention, and preferably constitute the surface layer
in contact with the paper sheet. Whether the fabric
is a single layer or multiple layer, the bicomponent
fibers are to be arranged in an orderly non-random
manner. By arranged in an orderly non.-random manner,
it is meant that fibers of a clothing run in a first
direction; the first direction fibers do not intersect
with other fibers running in the first direction; and
that fibers of the clothing run in a second direction;
the second direction fibers do not intersect with
other fibers running in the second direction; that
fibers running in the first direction intersect with
fibers running in the second direction, and vice
versa. For instance, fibers arranged in the machine
direction will not intersect with each other and such
fibers will intersect only with fibers running in the
a cross machine direction. It is preferred that the
clothings of the present invention be constructed of
fibers running in the machine or cross machine
direction, but such clothings could be constructed
of
fibers which run in directions that are at angles to
7
CA 02237964 2001-09-19
the machine and cross machine direction of a paper making
machine.
Therefore, in accordance with the present
invention, there is provided a composite yarn of a first
high modulus filament material and at least a second
filament material, wherein the first high modulus
material is covered within the second material, comprised
of
a first high modulus filament material;
a second bicomponent filament material, the
second bicomponent filament material having a sheath
component and a core component, wherein the second
bicomponent filament material is covered around the first
high modulus filament material and encases the first,
high modulus material along the length of the composite
yarn.
Also in accordance with the present invention,
there is provided a fabric for use in the forming,
pressing, or drying sections of a paper making machine,
the fabric having at least one layer, the at least one
layer being comprised of a composite yarn of a high
modulus material and at least a second material, wherein
the high modulus material is covered within the second
material, comprised of:
a first interior yarn layer of high modulus
filamentary material;
a second yarn layer of a bicomponent
filamentary material, the bicomponent filamentary
material having a sheath component and a core component,
wherein the bicomponent filamentary material is covered
around the first, high modulus filamentary material and
encases the first, high modulus filamentary material
along the length of the composite yarn.
Brief Description of the Drawings
Figure 1 is a composite braided fabric of the
present invention.
8
CA 02237964 2001-09-19
Figure 2 is another composite braided fabric of
the present invention.
Figure 3 is a cross section of a yarn of the
present invention.
Detailed Description of the Preferred Embodiment
Figure 1 is a fabric comprised of yarns of the
present invention. The fabric is a plain weave
construction, with yarns in the warp and shute direction
being comprised of yarns of the present invention. It can
be observed from Fig. 1 that the yarns are interconnected
with other yarns at the points at which the yarns
intersect. This is attributable to heat fusion of the
yarns, wherein the sheaths of the bicomponent materials
fuse to each other after heating the fabric to a
temperature above the melting point of the sheath
material, yet lower than the melting point of the core
material.
Both the warp and shute yarns of the fabric
shown in Figure 1 are of the same structure. The high
modulus interior of the yarns are about 134 filaments of
Kevlar~ 49. Eight bicomponent yarns have been braided
around the Kevlar~ interior. Each yarn is constituted of
sixteen (16) bicomponent filaments. The filaments are
Bellcouple~ from Kanebo, 250 denier, 16 filament count
having a low melt copolyester sheath material and a
polyethylene terephthalate) core, with the melting point
of the copolyester sheath being lower than the melting
point of the PET core.
8a
CA 02237964 1998-OS-15
WO 98/12371 PCT/US97/16505
The eight bicomponent yarns are braided around
the Kevlar~ interior. Braiding forms a relatively
stable structure, and the covered high modulus yarns
can be used to form fabrics as shown in Figure 1.
Such fabrics are formed according to methods readily
appreciated to one skilled in the art. After the
fabric has been formed, it is placed under tension,
heated to a temperature greater than the melting point
of the sheath, yet lower than the melting point of
the
core, and then. cooled to a temperature lower than
the
melting point of the sheath.
Due to the improved stability of the fabrics of
the present invention, it is believed that a single
layer fabric constructed of the composite yarns of
the
present invention could successfully run on a paper
making machine. That is, the present invention
provides a means fox producing single layered fabrics
able to withstand the demanding conditions which paper
machine clothings are subjected to.
Generally, fabrics must be constructed of at
least two layers to insure that the fabrics have the
necessary dimensional stability and strength in order
to withstand the demanding running conditions. Yet
because the paper machine clothings of the present
invention are characterized by high modulus, low
stretch materials, the stiffness and dimensional
stability of the fabric is provided by the layer of
high modulus materials and accordingly, one layer
fabrics are possible. In other words, because of the
high degree of strength provided by such materials,
it
is possible to use less material in constructing a
fabric while imparting equal ox even greater strength
when compared to multi layer materials which contain
considerably more material. Achieving a single layer
fabric design would be a substantial breakthrough in
9
CA 02237964 1998-OS-15
WO 98/12371 PCT/LTS97/165OS
PMC design. As machine speed increases, reducing the
amount of time for drainage, the ability to achieve
the smallest possible caliper becomes more
significant, since a single layer fabric would be
thinner than a multi-layer fabric, reducing the
distance liquid must traverse in order to drain.
The present invention could also be used as the
top laminate structure of a multilayer~structure, and
it is believed that its use as such a layer would
offer advantages over conventional materials due to
increased planarity on the surface. Tncreased
planarity is the result of reduced knuckle size at
points where yarns intersect. Upon heat fusion of the
fabric, the low-melt component of the bicomponent
fiber collapses and flows, reducing the knuckle size
of the crossover points.
The present invention may also be used as the
base layer of a multilayer structure. The improved
dimensional stability of this layer makes it well-
suited for this usage. Thus, other materials, such as
those of fine diameters, can be used in other layers,
since stability and strength is imparted by the layer
constructed of the high modulus material. The use of
fine diameter materials in paper-sheet contacting
layers would improve surface smoothness, a desirable
feature of paper machine clothings.
Figure 2 shows a fabric wherein the yarns
described in relation to Figure 1 above are used in
the warp direction. The shute direction yarns are
comprised of 9 ply material. That is, they are a ply
of nine yarns of bicomponent material as described in
Figure Z. The plied yarns are twisted loosely
together. The yarns have a distinctly flattened
appearance. That is, after heat fusion, the yarns .
take on a ribbon like appearance.
CA 02237964 1998-OS-15
WO 98/12371 PCTlUS97/16505
Figure 3 shows a cross section of a composite
yarn according to the present invention. The Kevlar~
interior is visible as a distinct region. The
bicomponent exterior is not discrete.
When running on a paper making machine, a fabric
according to the present invention should remain
cleaner than a clothing comprised of conventional
monofilaments. Heat fusion of a fabric comprised of
bicomponent fibers are characterized in part by fused,
intersecting yarns. In contrast, conventional
monofilaments have interstices at points where yarns
intersect. Fusion at the intersections of bicomponent
fibers diminishes, and possibly eliminates, such
interstices. Interstices are pinch points at which
debris can be entrapped and collect over time.
Accordingly, the heat fused intersecting yarns
produced with bicomponent fibers provides a structure
that should remain relatively cleaner than a clothing
comprised of conventional monofilaments.
Another advantage that paper machine clothings of
the present invention are believed to possess over
conventional clothings comprised of monofilaments is
that such clothings exhibit relatively planar, knuckle
free surfaces at cross over points. It can be readily
appreciated that when fibers are woven (or knitted},
knuckles are formed which diminish surface smoothness
.
As noted, knuckle size is reduced upon heat fusion of
the bicomponent fibers, which improves the surface
smoothness. Surface smoothness is a factor which
affects paper quality. Accordingly, clothings of
improved smoothness are of interest to the
manufacturer of paper and related products. A network
of bonds between intersecting fibers will be formed
upon heat fusion of a clothing comprised of
bicomponent fibers. Physical bonding of this kind
11
CA 02237964 1998-OS-15
WO 98/12371 PCT/US97J16505
will improve the dimensional stability over a
conventional clothing constructed of monofilament.
Because of the nature of bicomponent fibers and the
unique structures they may form, fibers of denier
lower than those for required for conventional
monofilaments can be used. The use of lower denier
fibers offers the advantage of a clothing thinner than
a clothing comprised of conventional monofilament,
without sacrificing fabric strength.
12
